lender etal



Jan. 28, 1964 R. J. LENDER ETAL PERMANENT MAGNET CORE TYPE ELECTRICAL INSTRUMENT Filed Jan. 5, 1961 2 Sheets-Sheet l ROBE/77d. LENDER JOHN GUGL/OTTA INVENTORS BY WgZ-E A ORNE Y 23, 1964- R. J. LENDER ETAL 3,119,962

PERMANENT MAGNET CORE TYPE ELECTRICAL INSTRUMENT Filed Jan. 5, 1961 2 Sheets-Sheet 2 ROBERTJ. LENDER JOHN sue/.10 7' 7'A INVENTORS A OR/VE Y United States Patent 3,113,962 PERMANENT MAGNET CORE TYPE ELECTRICAL HNETRUMENT Robert J. Lender, Cranford, and John Gugliotta, Clark, N.J., assignors, by mesne assignments, to Daystrom Incorporated, Murray Hill, N .J a corporation of Texas Filed Jan. 5, 1961, Ser. No. 8tl,783 3 Claims. (til. 324-151) This invention relates to an electrical instrument and more particularly to a moving coil electrical instrument of the permanent magnet core type.

Moving coil instruments having a permanent magnet core are well known in the art and comprise a transversely magnetized, generally cylindrical-shaped core and a soft iron yoke which acts as a return path for the magnetic flux. An annular air gap is defined by the outer periphery of the core magnet and inner walls of the soft iron yoke. A movable coil is arranged to rotate in the said annular air gap, the coil being carried by bearings supported in bearing supporting arms, or brackets, adjacent the opposite ends of the core magnet. The bearing brackets in the instrument of our invention comprise an integral part of a movement bracket to which the yoke and core magnet are secured.

The core magnet is cemented, or otherwise secured, to the movement bracket between a pair of projections formed on the bracket for accurate location thereon. The yoke comprises a generally U-shaped block having opposed pole faces formed on a pair of parallel arm portions thereof, and a transverse base interconnecting the said arm portions. An inner flat face portion of the base of the yoke abuts a fiat face portion formed on the outside end of the lower bearing supporting arm. A novel bushing assembly comprising an internally and externally threaded cylindrical-shaped member having an external radially extending flange formed thereon, is used to fasten the yoke to the movement bracket with the above-mentioned flat surfaces on the bracket and yoke in abutting relation. Dowel pins accurately locate the front end of the yoke with respect to said movement bracket. In addition to securing the yoke to the movement bracket, the said bushing member functions as a support for the lower jewel screw, as well as a spring abutment securing means.

An object of this invention is the provision of an instrument magnetic system in which the component parts thereof are inexpensively manufactured and easily assembled and adjusted.

An object of this invention is the provision of an instrument magnetic system comprising a movement bracket having bearing supporting arms integrally formed thereon, the said movement bracket including means formed thereon for easily and accurately locating a movable coil, a core magnet, and a soft iron yoke relative thereto, a bushing secured to the movement bracket and extending through a hole formed in the end of the yoke, and a locking nut clampingly securing the yoke to the bracket.

These and other objects and advantages will become apparent from the following description when taken with the accompanying drawings. It will be understood, however, that the drawings are for purposes of illustration and are not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the appended claims.

In the drawings wherein like reference characters denote like parts in the several views:

FIGURE 1 is a front view of an instrument mechanism embodying our invention removed from the case;

FIGURE 2 is a sectional view taken on line 2-2 of FIGURE 1;

FIGURE 3 is a rear view of the instrument mechanism shown in FIGURE 1;

FIGURE 4 is a side view of the movement bracket with the core magnet secured thereto;

FIGURE 5 is a top view of the movement bracket;

FIGURE 6 is a front view of the generally U-shaped yoke; and

FIGURE 7 is a sectional view taken on line 7--7 of FIGURE 6.

Referring to the drawings, the instrument illustrated comprises a substantially cylindrical-shaped permanent magnet core 11 and a generally U-shaped yoke 12 of soft-iron, or the like, having a pair of spaced parallel arm portions 13, 13 interconnected by a transverse base 14. The transversely-magnetized core 11 is positioned between the arm portions 13, 13 of the yoke a spaced distance therefrom. The inner walls of the arms 13, 13 are curved whereby an annular flux gap is defined by such curved walls and the outer periphery of the core. A wirewound movable coil 16 wound upon a coil frame 17 of suitable non-magnetic material operates within the annular flux gap. The yoke 12 provides a return path for the magnetic flux of the magnetized core.

The wire wound movable coil 16 carries a pointer '70 which cooperates with a suitably calibrated scale plate, not shown. Pivot staffs 18, 18 are secured to the ends of the coil 16 and are supported in jewel bearings 19, 19 contained in conventional jewel screws 21, 21. One jewel screw 21 is threadedly engaged in an upper bushing assembly 22 secured to a top bearing supporting arm 23, while the other jewel screw 21 is threadedly engaged in a lower bushing 24 secured to a bottom bearing supporting arm 26. The bearing supporting arms 23 and 26 comprise an integral part of a movement bracket 27 which includes an axially extending arm portion 28 integrally formed with the bearing supporting arms 23 and 26, upon which the core magnet 11 is secured as by cementing, or other suitable means; the arm portion 28 including an arcuate surface 29 of the same radius of curvature about the instrument axis as the magnet 11, to which surface 29 the magnet is secured. A pair of inwardly, generally radially extending projections 31, 31 are formed on the arm portion 28 adjacent the ends of the arcuate surface 29 between which the core magnet 11 snugly fits to insure accurate placement of the magnet on the movement bracket. The movement bracket is obviously made of a suitable non-magnetic material.

The movable coil 16 rotates through an angle which varies with the magnitude of the current flowing in the coil 16. In accordance with well-known instrument practice, upper and lower spiral hair springs 32 and 33 surround the respective upper and lower pivot assemblies, with one end of each spring being connected through spring abutments 34 and 36 to the coil. The outer end of the springs 32 and 33 are attached to spring abutments 37 and 38, respectively, which are carried by the bushing assemblies 22 and 24. Since the spiral springs are used to carry electric current to the coil, it is necessary to insulate the current connection to one of the springs from the connection to the other spring. To this end, the bushing assembly 22 has a pair of insulating washers 39, 39 on opposite sides of the spring abutment 37. The abutment 37 has a hole diameter significantly larger than the outside diameter of the bushing assembly 22 over which the abutment fits to insulate the abutment from the bushing assembly. The two-piece bushing assembly 22, comprising the inner and outer bushing portions 41 and 42 are staked, or otherwise suitably secured together and to the bearing supporting arm portion 23 of the movement bracket with the inner hub portion 41 extending through a hole formed in the arm 23.

' 3 In accordance with our invention, the lower bushing 24 serves three distinct functions, i.e., (1) a support for the abutment 38, (2) a support for the jewel screw 21 and, (3) a means for clampingly securing the yoke 12 -tothe movement bracket-27. The spring abutment 38 is shown positioned between a flange 44 formed on the bushing 24 and the arm 26 of the movement bracket, with the bushing 24 staked as at 46, or otherwise suitably securedto the arm-portion 26.

Inthe assembly of the instrument, the core magnet 11 with attached pole pieces, if any, is preferably first cemented, -or otherwise suitably secured, to the die cast movement bracket 27 containing the bushings 22 and 24 :and jewel screws 21, 21. The coil is then rotatably mounted within the bearings 19, 19 of the jewel screws, with the spiral springs and spring abutments included thereon. This assembly, which includes the bracket 27, magnet 11, movable coil 16 and associated parts such as the hair springs and abutments may be inspected and the necessary adjustments made thereto without the yoke 12 thereon to obscure and hamper such inspection and adjustment.

The hub 24 is provided With an externally threaded portion 47 which extends rearwardly of the arm portion 26 of the movement bracket 27 and through a clearance hole 48 formed in the base portion 14 of the yoke 12. A nut 49 is'tightened onto the threaded portion 47 of the bushing which extends through the clearance hole 48, and clampingly secures the yoke 12 to the movement bracket 27. The top, or free end portion of the arms 13, 13 of-the yoke 12 are provided with axially extending dowel pins 51, 51 (FIGURES 6 and 7) which fit into holes 52, 52 (FIGURES 4 and 5) formed in a rear- Wardly facing wall 53 on the movement bracket. Depending upon the dimensions and dimensional tolerances of the yoke 12 and movement bracket, either the surface 53 will abut the top face surface 54 on the yoke, or the bottom inside surface 56 of'the transverse base portion 14 of the yoke '12 will abut the rearward face 57 of arm 26 of the bracket 27 upon tightening of the nut 49.

Since-a greater surface contact is provided between the faces 56 and 57. The holes 53 and '59 in the top and bottom arms 23 and 26 for the reception of the bushing's 22 and 24, respectively, within which the jewel screws are mounted, may'be easily and accurately lo- 'cated with respect to'the arcuate surface 29 on thebrack- 'et 27 inthe manufacture of such bracket. 'Hence, the

coaxial'position of the coil, WhiCh'PiVOtS in the bearings of the jewel screws, an'dcore magnet axis is easily obb tained with a minimum of expensive close tolerance ma chine operations.

Having now described our invention in detail, in accordance with the requirements of the patent statutes, various changes and modifications will suggest themselves to those skilled in this art, and it is intended that such changes and modifications shall fall within the spirit and scope of the invention as recited in the following claims.

We claim:

1. An electrical instrument of the type including a generally cylindrical-shaped transversely magnetized core, a magnetic yoke comprising a pair of generally parallel extending arm portions formed with opposed pole faces and a transverse base interconnecting the said arm portions, a unitary movement bracket comprising first and second spaced bearing supporting arms interconnected by an axially extending arm portion, first and second bushings secured to the respective first and second bearing supporting arms, bearings supported by the bushings, means securing the core to the axially extending arm portion of the movement bracket, a coil pivotably supported in the said bearings for angular movement about an axis extending through the core, dowels extending between aligned holes formed in the free end face of the yoke arm portions and the movement bracket to relatively locate the said arms and bracket, means forming a clearance hole in the base portion of the yoke through which hole the second bushing extends, and means engaging the second bushing and clampingly securing the yoke to the movement bracket.

2. The invention as recited in claim 1 including a pair of spiral springs connected to opposite ends of the coil, and a pair of spring abutments mounted on the bushings and connected to the other end of the said spiral springs.

3. A magnetic system for an electrical instrument comprising a core, a movement bracket having a pair of spacedbearing supporting arms interconnected by an axially extending arm portion, means securing the core to the said axially extending armportion of the movement bracket, a generally U-shaped yoke having a pair of parallel extending arm portions interconnected by a transverse base portion, a bushing secured to one of the said bearing supporting arms and extending through a clearance hole in the base portion of the :yoke, means engaging the bushing and clampingly securing the yoke to the movementbracket, and dowels extending between the free end faces of the yoke arm portions and the movement bracket to relatively locate the same.

References Cited in the file of-this patent UNITED STATES PATENTS 2,518,609 Fogle Aug. 15, 1950 2,840,767 Ammon June 24, 1958 2,940,045 Ammon June 7, 1960 

3. A MAGNETIC SYSTEM FOR AN ELECTRICAL INSTRUMENT COMPRISING A CORE, A MOVEMENT BRACKET HAVING A PAIR OF SPACED BEARING SUPPORTING ARMS INTERCONNECTED BY AN AXIALLY EXTENDING ARM PORTION, MEANS SECURING THE CORE TO THE SAID AXIALLY EXTENDING ARM PORTION OF THE MOVEMENT BRACKET, A GENERALLY U-SHAPED YOKE HAVING A PAIR OF PARALLEL EXTENDING ARM PORTIONS INTERCONNECTED BY A TRANSVERSE BASE PORTION, A BUSHING SECURED TO ONE OF THE SAID BEARING SUPPORTING ARMS AND EXTENDING THROUGH A CLEARANCE HOLE IN THE BASE PORTION OF THE YOKE, MEANS ENGAGING THE BUSHING AND CLAMPINGLY SECURING THE YOKE TO THE MOVEMENT BRACKET, AND DOWELS EXTENDING BETWEEN THE FREE END FACES OF THE YOKE ARM PORTIONS AND THE MOVEMENT BRACKET TO RELATIVELY LOCATE THE SAME. 